The present invention principally relates to a treatment of silicate minerals to reduce their harmful properties by converting the silicate minerals to metal-micelle silicates. More specifically, the invention relates to a treatment of the silicate mineral asbestos to reduce its harmful properties by converting the asbestos to metal-micelle asbestos. The invention also relates to technological applications of both the metal-micelle silicate compositions and the presently disclosed method for making such silicate compositions. In addition, the invention relates to a method for lowering the magnetic rating of iron-containing silicate minerals such as asbestos, and to a method for reducing the environmental hazards associated with packaging and shipping of dry silicate minerals.
In general, a silicate includes any of the widely occurring compounds containing silicon, oxygen, and one or more metals, with or without hydrogen. More specifically, silicate minerals comprise the bulk of the outer crust of the earth and form in a wide range of geologic environments. All silicate minerals are built of a fundamental structural unit, the so-called SiO.sub.4 tetrahedron.
The crystal structure may be based on isolated SiO.sub.4 groups or, since each of the four oxygen ions can bond to either one or two silicon (Si) ions, on SiO.sub.4 groups shared in such a way as to form complex isolated groups or indefinitely extending chains, sheets, or three-dimensional networks. Mixed structures in which more than one type of shared tetrahedra are present also are known.
Silicate minerals are classified according to the nature of the sharing mechanism, as revealed by x-ray diffraction study, and an abbreviated form of such a classification is given below.
______________________________________ Nature of Si-O Type linkage Si/O ratio Examples ______________________________________ Nesosilicates Isolated SiO.sub.4 1:4 Olivine, garnet groups Sorosilicates Isolated com- 2:7, 6:18, Thortveitite, pound and so on beryl groups, Si.sub.2 O.sub.7, Si.sub.6 O.sub.18, and so on Inosilicates 1-Dimensional 1:3, 4:11 Amphiboles, extended and so on pyroxenes chains and bands Phyllosili- 2-Dimensional 2:5 Mica, clays cates extended talc, chlorite sheets Tectosili- 3-Dimensional 1:2 Feldspars, cates network feldspath- oids, zeolites ______________________________________
Many silicate minerals are of economic importance. Among the clays, feldspars, and refractory minerals, andalusite and wollastonite are used in the ceramic industries, mica as an electrical insulating agent, asbestos and exfoliated vermicularite as thermal insulating agents, and garnet as an abrasive. Talc is a constituent of facial powder. Other silicates are important as ore minerals, beryllium being obtained from beryl, zirconium and hafnium from zircon, and thorium from thorite. Some silicate minerals such as jadeite and nephrite are prized as ornamental materials, and peridot, garnet, tourmaline, and aquamarine are well-known gem stones.
Various health hazards arise, however, from the inhalation of natural silicate mineral dusts. In general, silicate minerals are notorious for causing lung diseases such as silicosis. A particular manifestation of silicosis is the black lung disease coal miners contract from inhalation of coal dust and crystalline silicates.
A particularly troublesome silicate mineral is asbestos. Asbestos is a commercial term applied to several minerals which are widely utilized, primarily because of their fibrous characteristics. All asbestos minerals consist of partially open bundles of very fine fibres and most single fibrils have a channel in the center. The principal asbestos minerals are chrysotile, crocidolite, amosite and anthophyllite. Because they differ in chemical and physical properties, these minerals have different commercial applications.
Chrysotile is the serpentine variety of asbestos fibre. Chrysotile fibres occur in a wide variety of shapes. The empirical composition of chrysotile is: 3MgO.2SiO.sub.2.H.sub.2 O. The unit cell, however, has been represented as Mg.sub.6 (OH).sub.8 Si.sub.4 O.sub.10. Chrysotile forms of asbestos comprise about 95% of the world's production and are principally supplied by Canada and Rhodesia, although there are some new and relatively small sources in the United States.
All varieties of asbestos other than chrysotile belong to the amphibole group of minerals and are generically termed amphibole asbestos. The amphibole asbestos are straight fibres and are further characterized by perfect prismatic cleavage with angles of 56.degree. and 124.degree. between cleavage planes.
The empirical composition of crocidolite is Na.sub.6 Fe.sub.10 Si.sub.16 O.sub.46 (OH).sub.2. Crocidolite is the fibrous form of the mineral reibeckite. Crocidolite fibres, having an elliptical or circular cross-section, are flexible and stronger than those of chrysotile. The principal source of crocidolite is the Union of South Africa.
The empirical formula of amosite, a yellowish-grayish white variety asbestos found only in Transvaal, South Africa, is (FeMg.sub.7)Si.sub.8 O.sub.22 (OH).sub.2. Amosite fibres, which exhibit a rectangular section, are harsher and ordinarily slightly weaker than those of chrysotile. Amosite fibre lengths extend to 10-11 inches.
The empirical formula of anthophyllite is Mg.sub.7 Si.sub.2 O.sub.22 (OH).sub.2. If unexposed to the atmosphere, anthophyllite is a greenish-gray color. On being exposed to the atmosphere, however, it yields brownish-white fibres that are short and weak and are only slightly flexible. Anthophyllite is found in Georgia and North Carolina in the United States and also in Finland.
Because of their physical and chemical properties, the asbestos minerals are extremely useful materials, presently employed in more than two thousand applications, including fireproof textiles, brake linings, thermal insulation, asbestos cement pipe, asbestos-cement sheets, paper products, gaskets, woven fabrics, high temperature insulation, chemical-resistant filters, and filler material.
Recently discovered evidence indicates, however, that introduction of asbestos into living organisms increases the organisms' risks of developing various chronic diseases, including lung cancer, chronic fibrosing processes in the lungs, and mesothelioma of the lungs or intestines. The gravity of this evidence is underscored by the widespread applications of asbestos and the resulting frequent exposure of living organisms thereto.
It is presently believed that when an asbestos fibre comes into contact with a living cell, the asbestos fibre irritates the cell and leads to its eventual weakening. After such weakening, it is believed the asbestos fibre enters into the cell.
Although it is not clear what happens when asbestos enters a cell, in the article entitled "Relationship Between Exposure to Asbestos, Collagen Formation, Ferruginous Bodies and Carcinoma," published by the inventor in the November 1974 edition of the American Industrial Hygiene Association Journal, it is postulated that entrance of asbestos into living cells results in formation of ferruginous bodies. A ferruginous body is an iron-containing protein body with a fibrous core thought to be formed by macrophage cells attempting to phagocytize a foreign fibre.
Ferruginous bodies formed in living organisms appear to occur in various shapes and sizes, including evenly distributed deposits, series of clump-like deposits, and large barbell-shaped deposits. Although sizes vary, the fibre core approximates the lengths and diameters of asbestos and other fibres found in living organisms.
It is further theorized that formation of a ferruginous body in a living cell occurs by deposition of ferritin, a crystalline iron-containing protein and/or hemosiderin, a yellowish-brown granular pigment formed by the breakdown of hemoglobin and composed essentially of ferric oxide, on an electronegative surface, such as the nucleophilic silicates present in asbestos fibres. The formation of ferruginous bodies in a living organism appears to set in motion a collagen synthesis ultimately resulting in chronic fibrosis and a potential for developing carcinoma.
Those skilled in the art have diligently sought a method for rendering asbestos less harmful without substantially affecting its significant physical and chemical properties.
Other problems associated with asbestos and other silicate minerals have plagued the art. Those in the industry have previously dry processed asbestos because the material does not handle well wet. Handling asbestos in a dry state creates asbestos dust and thus increases the possibility of introduction of asbestos into a living organism. To combat this danger, many safeguards are presently employed to prevent inhalation during the handling of asbestos. For example, expensive machinery, such as automatic bag opening machines, is frequently used. There exists, therefore, a need for a wet asbestos-like material and other silicate mineral-like materials which handle well.
Another problem of increasing concern is contamination of water supplies by asbestos fibres and other silicate minerals, particularly in areas where waste from asbestos cement plants, mines, or other processes involving asbestos or other silicate minerals comes into contact with the water supply.
Further, although unrelated to rendering asbestos less harmful, the magnetic rating of certain iron-containing silicate minerals, such as grades 4-7 of untreated asbestos, which are used in reinforcing cement and as binding agents, is too high to allow use of such asbestos as an effective electrical insulator in many applications. Decrease of the magnetic rating of such asbestos would decrease the electrical conductivity thereof and allow an expanded use of such treated asbestos grades in applications such as electrical insulating tape.
The present explosive growth in use of asbestos, moreover, compared to the rate of discovery of new sources thereof, raises the spectre of depletion of this valuable mineral by the year 2000. This danger is compounded because some portion of the existing asbestos sources cannot presently be used owing to environmental restrictions. There is, accordingly, a pressing need for a treatment of asbestos which would decrease the total use of natural asbestos fibre while at the same time facilitating use of sources of asbestos now subject to environmental restrictions.
Another problem facing technological workers involves the economic removal of acidic iron from sources such as aqueous mine drainage. Although solutions to this problem would, at first blush, seem irrelevant to methods for treating silicate minerals, including asbestos, the present invention offers a highly attractive solution to the removal of iron from aqueous solutions.
In accordance with the present invention it has been discovered that treating silicate minerals, prior to their introduction into a living organism, with an aqueous metal salt solution to form a metal-micelle silicate renders the silicate less harmful to living cells. Specifically, it has been discovered that treating asbestos, prior to its introduction into a living organism, with an aqueous metal salt solution to form metal-micelle asbestos masks the iron-binding sites in the asbestos. Hence, the metal-micelle asbestos, when introduced into a living cell, do not react with cellular iron. Accordingly, the reaction that is believed to initiate fibrosis is blocked and biological hazards associated with exposure of living organisms to asbestos are reduced. Moreover, the treatment of the present invention, in addition to rendering asbestos less harmful, provides an asbestos-like material having physical and chemical properties, such as insulating properties, reinforcing strength, binding properties and numerous additional properties, very similar to those of untreated asbestos.
The present invention thus makes it possible to replace untreated asbestos fibre by a less hazardous but equally-useful composition of matter, metal-micelle asbestos, in the multitudinous processes and products presently utilizing asbestos.
Representative applications of the metal-micelle asbestos and other metal-micelle silicates of the present invention include:
______________________________________ 1. Treatment of gravels or geological deposits containing asbestos or silicate minerals with a micelle-forming solution, particularly sandstones and granites. 2. Surface applications of micelle-forming solutions to existing open sources of asbestos and other silicate minerals, such as in schools, homes, offices, and recreation areas. 3. Brake-linings, gaskets, and other devices subject to friction and stress. 4. General uses as a binding agent and extender, in- cluding use as an extender and coloring agent in paint. 5. Cement. 6. Yarn spun for producing woven cloth for curtains, bags, ribbons, filters, protective coverings, etc. 7. Formation into paper or board. 8. Fluffing to form an insulating material. 9. Marine boiler insulation. 10. Treatment of demolition debris and reuse in cements and pavings. ______________________________________
Moreover, the present invention comprehends treatment of asbestos and other silicate mineral hazards already in use. For example, a playground covered by gravel containing asbestos can be made less harmful simply by spraying the gravel with an appropriate metal salt aqueous solution.
The present invention also can provide both a wet asbestos-like material and a wet asbestos which handles well and which can be shipped and used as a wet cake. In addition to providing the handling advantages inherent in use of a wet cake or slurry, using the material in the form of a wet cake or slurry reduces the potential biological risks resulting from the exposure of workers to asbestos dust during dry processing.
In addition to diminishing the likelihood of the reaction that initiates fibrosis and eventuates in cancer, the metal-micelle asbestos fibres of the present invention have a slightly larger diameter than untreated asbestos fiber. This slight increase in diameter makes the metal-micelle asbestos fibres less respirable than conventional asbestos, i.e., less apt to be retained in the lungs of a living organism.
Treatment of asbestos by the method of the present invention to form a metal-micelle asbestos can increase the total weight of asbestos-like material, with an attendant decrease in the use of natural asbestos fibre in certain applications. The formation of metal-micelle asbestos, moreover, may well allow use of sources of asbestos previously subject to environmental restrictions. Accordingly, the present invention may decrease the depletion rate of world supplies of useable asbestos.
Further, the present invention provides a means for decontaminating water supplies containing asbestos fibres and other silicate minerals. Addition of an appropriate metal salt to the water removes the silicate mineral contaminant by converting it to a metal-micelle silicate.
The metal-micelle asbestos of the present invention has a lower magnetic rating than untreated asbestos. The present invention also decreases the magnetic rating of iron-containing silicates which are not converted to metal-micelle silicates. Thus, with respect to the silicate asbestos it will be possible to use additional grades of asbestos, as well as asbestos metal-micelles, in such applications as electrical insulating tape.
The present invention also provides an economical method for removing acidic iron from such sources as aqueous mine drainage. By contacting the mine drainage with a silicate, mineral such as, for example, an asbestos mat in the presence of ammonia, the iron contained in the drainage will precipitate onto the asbestos mat to form iron-micelle asbestos.